Currently, Rice MCS's occupy a middle ground, somewhere between undergrads and PhD's: They have on-campus mailboxes, longer library checkout times, and something like an office, but they don't get paid, take mostly undergrad classes to start, can't get into Herman Brown late at night, etc. In the past some MCS's have complained about being ``in the dark'' as far as getting good advice about courses, requirements, etc. Hopefully, your stay will be a bit easier thanks to their efforts. The most important thing to do is make sure you have the current list of requirements for the MCS degree. If not, make sure you get it from the department. That counts more than any advice we could give here.
You are entitled to a department mailbox, where almost everything important (i.e. grades, library late notices) will be sent (NOT to your permanent address).